Ceramic filter filtration is becoming more and more common because people have higher and higher requirements for the quality of aluminum products. The ceramic filter for casting can not only effectively remove a large number of oxide inclusions in molten aluminum, but also filter out a few microns of small inclusions which can not be achieved by traditional technology.
As hydrogen atom, sodium, potassium, and other harmful ions in liquid aluminum are usually adsorbed on inclusions, and inclusions will become the core of bubble formation, so these harmful elements in inclusions can be reduced while filtering inclusions. Some studies have also shown that the ceramic filter filtration filters out many fine inclusions, thus reducing the effective nucleation required for solidification of molten aluminum, which can promote the nucleation and growth of molten aluminum under large undercooling conditions, and refine the structure.
Ceramic Filter Filtration
In general, there are three ways to remove inclusions from molten aluminum: precipitation, flotation, and filtration. When the size of inclusions is less than 90 m, they are less likely to settle to the bottom of furnace under the action of gravity. Traditional gas purification, on-line refining and other processes can make some inclusions float to the surface of molten aluminum, but when the size of inclusions is less than 30 μ m, the chance of floating is very small.
The advantage of the filter plate is that it can filter out inclusions much smaller than its pore size. The principle of inclusion passing through the filter plate can be attributed to three mechanisms: screening mode, cake mode and depth mode.
The most direct method to evaluate the quality of ceramic filter media is to detect the reduction rate of inclusion content before and after the aluminum liquid passes through the filter plate, that is, sampling and analysis.
This method actually measures the time required for molten aluminum to pass through the ultrafine graphite filter disc. When the container is evacuated, the time required to pass a certain amount of molten aluminum under atmospheric pressure is related to the cleanliness of the molten aluminum. Clean molten aluminum takes less time, while dirty molten aluminum takes longer. In addition, it can also be used to analyze the filtered graphite disc, and the size of inclusions retained on it can indicate the cleanliness of liquid aluminum.